The present invention relates to an improved infusion pump and a method for infusing patients using same.
During the course of medical treatment, drugs are necessarily administered to patients over a period of time (i.e., several minutes, hours, days). Rather than relying on the manual injection of bolus doses of drugs using syringes or on manually setting the drip rate of gravity-fed intravenous infusion sets, health professionals are utilizing infusion devices and systems that electronically or mechanically control the infusion rate of drugs as they are being administered to patients.
The most common application of infusion devices is for the maintenance of appropriate fluid levels in patients. Fluid therapy is commonly used in the treatment of burns, the pre- and postoperative management of surgical patients, and in the treatment of dehydration.
The administration of drugs provides the greatest challenge to infusion devices. For a drug to be effective, the concentration of any drug at its site of action must be sufficiently high for the drug to be effective, yet the concentration must not be too high for the drug to become toxic to the patient.
Widely used in differing applications such as delivering anesthetics during surgery, chemotherapy for cancer, and oxytocic agents for inducing labor, continuous drug infusion reduces the fluctuations in a drug's concentration that occurs with the more traditional modes of drug administration such as namely injections and pills. Moreover, continuous drug infusion assures a continuous therapeutic action as long as the infusion rate is appropriate.
Drug infusion systems consist of at least two components: 1) a mechanism that delivers the drug; and 2) a means of controlling the rate of delivery. A variety of devices are utilized by health care professionals for delivering drugs intravenously. An infusion pump is one such example.
Typically, with a powered infusion pump of the type similar to the Bard Infus O.R..TM. Pump (Bard MedSystems Division C.R. Bard, Inc., North Reading, Mass.), a predetermined volume of a drug is infused into a patient per unit of time as a function of the patient's body weight. The pump has a number of individual settable dials which include a dial for the infusion rate, the patient's body weight, and the bolus or initial dose of the drug being infused. For each drug that is delivered by an infusion pump to the patient, the bolus is typically calculated in micrograms per kilogram ("mcg/kg"). The infusion rate, also referred to as the maintenance dose, is calculated as micrograms per kilogram per minute ("mcg/kg/min"). The patient's body weight is generally calculated in kilograms ("kg").
Internally of a powered infusion pump, the settable dials have some relative setting position depending upon the degree of rotation of the external dial, and relate differently to each drug that is infused. As such, a different drug label plate is required for each drug when setting the external dials on the infusion pump.
With commercial infusion pumps like the Bard Infus O.R..TM. Pump, the difficulty occurs in that each drug has a different concentration and level of toxicity. The physician is, thus, required to first reference a drug card that is provided by the drug manufacturer in order to determine the appropriate induction bolus and continuous infusion rate for the drug.
As shown below, Table 1 represents a typical drug manufacturer's dosage reference card, which is a reproduction of a commercially produced dosage reference card of the general type provided to anesthesiologists to assist them in calculating the drug specific settings for the infusion pump. As shown for the drug DIPRIVAN.RTM. (propofol), the bolus dosage ranges from 1.00 mg/kg to 2.75 mg/kg with a recommended dosage of 2.0-2.5 mg/kg for healthy young adults. The patient's weight is also factored into the bolus dosage. Thus, for a patient weighing 77 pounds (35 kg) and at a drug dosage of 2.00 mg/kg, the recommended bolus dosage is 7 mL. The infusion pump dial corresponding to the bolus dosage would then be set to deliver the 7 mL. ##STR1##
A similar sequence of steps is followed by the physician when determining the appropriate continuous infusion rate for a drug. The infusion rate guidelines for DIPRIVAN.RTM. are shown in Table 2 below. For example, the continuous infusion rate for a patient weighing 77 pounds (35 kg) at a desired dosage of 10 mg/kg/h is 35 mL/h. The infusion pump external dial corresponding to the infusion rate is, thus, set at the desired rate of 35 mL/h. ##STR2##
Because of the vast number of drugs and the different concentrations at which each drug can be infused, physicians are inundated with numerous drug reference cards. Physicians tend to carry around the drug cards as a reference for setting the dials on the infusion pump, or alternatively, physicians commit to memory the various infusion guidelines for a limited group of drugs. A major disadvantage of the existing system is that errors occur when physicians attempt to memorize the various drug infusion guidelines. Further, the existing system encourages physicians to use the same group of drugs repeatedly to avoid learning new drug infusion guidelines. As a result, physicians are more likely to continue using the drugs and, thus, the drug infusion guidelines with which they are most familiar, rather than trying newly marketed drugs.